[llvm] [Offload] Don't create events for empty queues (PR #152304)

[Ross Brunton via llvm-commits]

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@@ -939,6 +939,14 @@ struct GenericDeviceTy : public DeviceAllocatorTy {
   Error printInfo();
   virtual Expected<InfoTreeNode> obtainInfoImpl() = 0;
 
+  /// Return true if the device has work that is either queued or currently
+  /// running
+  ///
+  /// Devices which cannot report this information should always return true
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RossBrunton wrote:

Yep, I was thinking of adding an `EMPTY` queue info, but figured it would be better as a seperate change.

Returning true if it's unsupported isn't great, but I assume there are backends we wish to support that don't support these kinds of queries. I'm not sure what better way there is.

https://github.com/llvm/llvm-project/pull/152304